Process for purifying gases



PROCESS FOR PURIFYING lGASES Filed Dec. 4, 1923 Patented Aug. 7, y1928.

PATENT OFFICE.

. WALTER H. rULWmLnn, or WALLINGronD, PENNSYLVANIAV AssIeNon rro 'run u. s. I. ooivrruic'rmci` coMPANY, or PHILADELPHIA, :enNNsYLvAnIm a couronn- TION 0F DELAWARE.

' PROCESS FOB P'URIFYNG GASES.

"appiattimiiea member 4. 192s. Vserial No. 678,431.

The principal object of the present invention is to economically and satisfactorily .remove hydrogen sulphide from illuminating and other gases by scrubbing and in such a.

W way that the scrubbing solution 'when foul is revivied `or fitted for re-use without pollution of the-surrounding atmosphere by hydrogen sulphide or other noxiousgases. Anotherfobject of the invention 1s to pro- 1 vide for recovering free sulphur from .the foul solution in the process of re-viviying it or ttingit for re-use.' L c To these and otherA ends hereinafter set forth the invention in'one of its as ects com- .15 prises the selective oxidization o theA foul solution, with deposition or liberation of sulphur as such, principally or 'essentially 'to a body or bodies capable of combining with or taking on hydrogen sulphide 1n the re-use of the solution as distinguished from a body or bodies lacking that capability. In another of lits aspects the invention comprises the provision` ofa scrubbing solution containing weak ,free 'acid and which, when subjectedato selective oxidization, gives rise to the production of more of the body or bodies capable of removing hydrogen sul-v phide from the gas inthe' scrubbing opera tionthan to a body or bodies lacking that au capability.' The invention further comrises the' process of revivifying or fitting ibut solutions for re-use which consists in spraying the same onto or passing them in film formy over catalytic material as coke'in the presence of air with deposition of sulphuras such. l 'p l In practice this process is used for the removal Aof hydrogen sulphide from illuminating gas and it is carried out by scrubbing the 40 gas with an aqeous solution ofv a salt that is .suciently alkaline to absorb hydrogen sulphide from-the gas, thusv forming a hydroy,I sulphide or foul i solution. In the second stage of theproc'ess the sulf-hydrate, hydrou aa sulphide or foul solution is passed in a layer sufiiciently thin or -film over some form of catalytic material (coke has been successv this is done in the presence of air so that .tu the oxygen of the air will react wth'the y `hydro-sulphide to the'end that the hydro'- sulphide is decomposed, yreforming the original salt and setting free sulphur. This y second stage of the process lmay-be referred `sulphate will be formed, while if it is still more violent sodium sulphate will be formed and y both these salts are inactive for re? moving hydrogen sulphide s o that the object is to cause the maximum amount of sulphur to go to free sulphur and the minimum amount to go to sulphate or other inactive salts in order that the process may be car-A ricd on with the minimum expenditure of sa ts.

If there is present in the solution an appropriete amount of free acid, such as boracic acid, the percentage of the salt going to thio-sulphate and sulphate will be reduced, and the percentage going to salts active in the removal of hydrogen sulphide from the as increases. However, if the percentage of ce weak acid is permitted to unduly increase,`

it will reduce the ability of the solution to absorb hydrogen sulphide. For example, if a solution of sodium tetra-borate (borax) is used, there will be built up the necessary amount of free acid as boracic acid and in continuing the operation or practice of the process the amount of free acid can be controlled by the addition to this solution, from' time to time, of vcheaper forms of sodium` salts such as sodium carbonate or soda'ash.

` In further describing the invention reference may be made to the accompanying drawing, the single figure of which illustrates diagrammatically 'and schematically and principally in central sectional elevation one orm of apparatus in connection with which thedprocess of the invention may be prac-4 tice A stream of gas flowing upwardly as from 2 to 3 in a tower 1 filled with some material 5 that will expose a large surface, such as coke, tiles and the like, 1s scrubbed with a downwardly flowing stream of absorbi -vby the addition of sodium carbonate or soda fully used and' it is cheap andavailable) and ash so that the titratable sodium ion present may be between 5 to 10 grams per liter, y

whileV the free boracic acid will be of the order of grams per liter. Such solutions will absorb from 40 to 60 grains of hydrogen sulphide per gallon,.and the amount of solution used per hundred feet of gas is I 650 grains of hydrogen sulphite 20 after which onl f to ta regard to theinitial amount present. Other-v wise expressed, for a coke oven gas containing er liter, it will be necessary to circulate a out 100 gallons of solution per 1,000 feet of gas in order to remove 600 grains of hydrogen sulphide per 100 feet of gas. The'process may l e well racticed at a temperature above 70 F. he solution introduced at 4 leaves the tower or scrubber purifier 1 at 6 entering the sump 7. f

In scrubbing commercial coke oven gas l5 which contains carbon dioxide and cyano en in addition to hydrogen sulphide, car on dioxide is absorbedyfor a short time at vthe beginning of the operation and until it comes into equilibrium with the solution a relativel small amount will be absorbe corresponding to the additionof fresh soda ash to the solution. In the case of cyanog'en it is absorbed, in case sodium salts are used, forming sodium cya- `nide, and a portion of this sodium cyanide combines with hydrogen sul hide forming sodium sulphocyanide so t at a certain amount of soda is consumed in making up this loss.

The solution which has absorbed hydrogen sulphide or, in other words, the foul solution from the sump 7 by the (pump 8 and by pipe 9 is sprayed over a be 11 of some catalytic material which will cause maximum $5 decomposition of the sodium hydrosulphide to free sulphur and minimum formation of sodium thiosulphate, sulphate or other salts which are inert or ineffective for further use in absorbing hydrogen sulphide. A bed con- 40 sisting of alayer of coke from 3 to 5 feet in delpth is eic'ient in causing this reaction evplace. From experience it appears that the rate of supply of the foul solution to the bed of'coke should be limited or con- '45 trolled. If the foul solution iss raved over the surface of the coke in too t ick a film,

the described reaction does not take place,

but if the film is suiliciently thin the reaction takes place very etliciently.` In this .way the rate can be ascertained readily and without undue experimentation. However, it may be said that a. rate of 71/2gallons per hour er square fodb of surface of the described d should not be exceeded for eicient re- 66 action. A certain 'amount of air must be available to the bed 11 in order to furnish the necessary oxygen to carry the reaction forward to completion. As shown this 'is done by drawing down through the opening' 00 12 in the chamber 11 and through the coke a small quantity of air as by the. blower 13.

This air supplies the necessary oxygen and when it issues from the bottom 14 of the layer 11, or from the outlet of the blower Il y13, it will be free from hydrogen'sulphide.

ganic acid, and heating to redness. It is not well to use too eicient a catalyst, for example, if vanadium be used the' formation-of sodium tho-sulphate or sodium sulphate is likely to be excessive.

At the start of the process the free sulphur formed in the reaction between the oxygen of the air and the ingredients of the oul solution in the presence of coke is absorbed by the latter but after a certain amount of sulphur has been thus absorbed the free Sul- A phur washes through and may be removed from the` solution and recovered by a filter press or equivalent apparatus. In the drawings the reviviied solution and the free sulphur pass from 14 into the sump 15, and the free sulphur is extracted as such by the filter .press 16 and its connections, and the revivified solution is passed by the Dump 17 to the pipe 4 for re-use. Temperatures above 70 F. are advantageous in decomposing the sodium hydro-sulphide to free sulphur.

Solutions of sodium carbonate alone may be used in this process or in factsolutions of any alkaline salt that will absorb hydrogen sulphide. -However, it appears that the presence of a free weak acid such as boraclc acid, which can be secured by starting wlth a solution of borax, opposes the formation of undesirable salts such Vas sodium thiosulphate and sodium sulphate 'and increases the percentage of free sulphur which may be recovered and consequently promotes the fitting of the solution or revivifying of the solution for ref-use in scrubbing hydrogen sulphide and other impurities from additional supplies of gas.

For the sake of further explanation it -foul solution, and this is referred to as indicating that the invention being in its nature chemical is obviously not to be limited to the precise procedure nor to the exact ingredients set forth or otherwise;than as the prior art and the appended claims and y the doctrine of equivalents appropriate in the case of chemical inventions may require.

I claim: 1. In the process for purifying gas by the v action of av solutionof a salt suiclently alkaline to absorb hydrogen sulphide as sulf-hydrate there y becoming foul, tsim- Lumens provement which consists in preferentially I oxidizing the sulf-hydrate principally to the ori inal salt with liberation of sulphur as suc by passing the foul solution in film form over coke in the presence of air.

2. In the process for purifying gas by the action of a` solution capable of absorbing hydrogen sulphide gas thereby. becoming foul, the improvement whichconsists in extraeting sulphur as such from the foulsolu`- tion by the aetionpf coke in the presencel of air thereby revivlfyng or ltting the soluv tion for re-use.

3. In the process of purifying gzts by the action of a solution of a salt suiiiciehtly alkaline to absorb h drogen sulphide as as sulphydrate there y becoming foul, t e improvement which consists in oxidizin sul hydrate principally to the origina salt wit liberation of sulphur as such by subjeotin` it to the action of air in limited quam.

tity a apted to produce free sulphur as disthe tinguished from driving olif free hydrogen i sulphide.

' WALTER H. FULWEILER. 

